1. Field of the Invention
The present invention relates to ultrasonic inspection techniques, and in particular relates to a non-destructive method and apparatus for inspecting materials at temperatures in excess of 500.degree. C.
2. Discussion of the Relevant Art
Ultrasonic measurement techniques have been used for many years to measure characteristics of materials and to inspect the materials utilizing a pulse echo method to locate and determine the magnitude of imperfections in the material. Utilizing known techniques, it is also possible to determine the thickness of material under test. However, the measurement of characteristics of materials at temperatures in excess of 500.degree. C. was developed recently. The technique utilized a high pressure dry coupling method to introduce the ultrasonic wave into the heated materials and typically measured the longitudinal and shear acoustic velocity of a material to determine its mechanical properties. The measurement device utilized a single transducer with a metallic delay line that incorporated some type of cooling so that the transducer could be kept within safe operating temperatures. The length of the metallic delay line was a limiting factor which determined the maximum thickness of the material that could be inspected. This is because the second multiple echo from the end of the delay line provides a practical limit beyond which echoes from within the material being tested are obscured. Practical systems utilizing this technique have been designed and they are capable of measuring thicknesses of materials up to about three and one-half inches (31/2").
One of the known systems is disclosed in U.S. Pat. No. 3,534,609 issued to H. W. Grenfell, et al on Oct. 20, 1970. The apparatus disclosed in the patent to Grenfell, et al is used to measure the temperature of a metal and requires the use of two delay lines (extension bars) disposed on either side of the material under test and in intimate contact therewith. The opposite ends of the delay lines have the transducers affixed thereon. The extension bars are surrounded by a jacket which has input and output ports designed to carry water for cooling these bars. The technique as disclosed requires that two surfaces of a material under test be contacted by the delay lines (extension bars) and requires that equal pressure be exerted on both bars in order to insure the transmission and reception of the ultrasonic signal into the material under test.
The present invention overcomes the shortcomings found in the art by providing a dual transducer and method which requires contact with only one surface of the material under test and thereby simplifies the measurement and is not limited by requiring access to multiple surfaces.